The present invention relates to a vehicle tire, a pneumatic vehicle tire in particular, especially for utility vehicles, with a tread that is provided with circumferential grooves, at least one of which is provided with a wiper rib member that extends around its entire circumference. A wiper rib member is a stay that is located approximately at the center of the base of the circumferential groove(s) and is designed to be integrally connected radially inwardly to the rest of the tread but not laterally. The wiper rib member, when viewed radially outwardly, is provided with two different portions; the upper portion of the wiper rib member is divided by grooves basically extending axially, whereas the wiper rib member is continuous in its lower portion.
Particularly with pneumatic vehicle tires for trucks the problem is known that stones or pebbles of a considerable weight can get stuck in the grooves that serve for draining water from the tread. The mastication on entering the contact patch favors a picking up of stones and their gradual transport radially inwardly. The migration of the stones can continue down to the base of the grooves, and the stones can even gradually penetrate the overlay provided on top of the belt plies.
In order to prevent such damages, many different measures have already been known. Among those, the simplest seems to be to incline the groove flank to a great extent relative to the radial such that the grooves significantly enlarge outwardly. However, this measure has the disadvantage that a considerable difference in the groove width across the radial is created, particularly in the case of the great tread depth of truck tires, usually 22 mm. This leads to the effect that the groove width of the tire as manufactured is unnecessarily large, the remaining tread positive unnecessarily small, and thus the decline of the tread depth during its lifetime is unnecessarily great. Economic efficiency, however, is of the greatest importance for the customer in this market sector.
Therefore, it is common to design the groove flanks to be significantly steeper; the common flank gradient relative to the radial ranges between 3.degree. and 6.degree..
However, in order to prevent damage to the belt plies by penetrating stones, it is common to provide an additional protuberance, called wiper rib member, at the base of the groove. There seems to be consent among the important tire manufacturers that wiper rib members operate satisfactorily. However, there is still a dissent in regard to the optimal design.
The two designs which are mostly known on the market are illustrated in FIGS. 1a and 1b, which belong together, and as well in FIGS. 2a and 2b which belong together. With the design schematically illustrated in FIGS. 1a and 1b, the wiper rib member is continuous over the tire circumference, whereas with the designs schematically illustrated in FIGS. 2a and 2b, the wiper rib member is divided by small transverse grooves (8). Furthermore, a combination of these two designs is known from French Patent 1,163,341.
U.S. Pat. 2,265,543 illustrates in FIG. 3 trapezoid-shaped wiper webs/wiper rib members 12. Between each two wiper webs 12 a trapezoid-shaped protuberance 11 is provided, each of which, radially inwardly and with one of its two sides, engages the positive engaging the road surface. The spacing between each two protuberances 11 which are sequently arranged in the circumferential direction and are located within the same circumferential groove, is larger than the circumferential extension of each protuberance 11.
In both of the aforementioned FIGS. 1a, 1b and 2a, 2b representing the prior art as well as in the following FIGS. 3-6 which illustrate the present invention, the vehicle tire is labeled as 1, the groove, preferably the circumferential groove that is to be protected, is labeled as 3, and the wiper rib member that is provided at the base 4 of the groove 3, is labeled as 5. The transverse grooves which divide the wiper rib member 5 are labeled as 8.
The object of the present invention is to improve the design of the wiper rib members known per se, also in regard to the related noise development.